Internal combustion engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of chemical compounds. The chemical compounds may be composed of gaseous compounds, which may include nitrous oxides (“NOx”), and solid particulate matter, which may include unburned carbon particulates called soot.
Due to increased attention on the environment, exhaust emission standards have become more stringent, and the amount of gaseous compounds emitted to the atmosphere from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. One method that has been implemented by engine manufacturers to comply with the regulation of these engine emissions is exhaust gas recirculation (“EGR”). EGR systems recirculate some of the exhaust gas byproducts into the intake air supply of the internal combustion engine. The exhaust gas directed to the engine cylinder reduces the concentration of oxygen within the cylinder and increases the specific heat of the air/fuel mixture, thereby lowering the local combustion temperature within the cylinder. The lowered local combustion temperature and reduced oxygen concentration can slow the chemical reaction of the combustion process and decrease the formation of NOx.
Maintaining the proper ratio of EGR to intake air is important in lowering local combustion temperatures and, consequently, NOx formation. As such, a reliable and accurate EGR flow meter, in conjunction with other engine components, helps achieve stringent NOx emission limitations.
Some engines with external EGR loops, such as the one disclosed in U.S. Pat. No. 6,786,210 (“210”), have separate EGR meters for measuring EGR flow. '210 discloses a venturi measurement sensor for measuring flow disposed within the EGR passage. The presence of a separate airflow sensor within the airflow loop, as disclosed in '210, unfortunately, results in extra hardware to the EGR loop. The extra hardware may lead to increased costs and pressure loss. Furthermore, many engines are constrained by tight space limitations, as there may be limited space available “under the hood” of an automobile. In some of these engines, the extra hardware may present problems in meeting these space limitations.
The disclosed flow meter is directed to overcoming one or more of the problems set forth above.